Project Summary
This innovative project completed feasibility studies for rooftop solar on 11 different sites in the Exeter City Council portfolio. All the sites were considered part of one cohesive project, with a single encompassing business case.
The rationale was that by combining the sites together, the additional costs of more complex sites are negated by the more ‘straight forward’ roof installations with higher rates of return. A business case can therefore be made for a higher number of sites with an acceptable Internal Rate of Return (IRR), and borderline projects are able to be taken forward.
Our Role
The project was awarded a grant by the South West Net Zero Hub as part of our Local Net Zero Fund to partly fund the work completed. The Hub also provided a critical friend role – providing guidance on defining the scope, reviewing technical documents, and providing advice to the project team.
Background
The project team procured a consultant to complete all the feasibility work needed to take the sites to “investment readiness”. This included:
- Project Definition
- Data Collection
- Planning Approval (Pre-Application)
- Preliminary Scheme Sizing
- Engineering Site Surveys
- Grid Connection Applications
- Conceptual Design
- Structural Engineering
- Fire Safety Consultants
- Roof Condition Surveys
- Glint & Glare Studies
- Landscape and Visual Assessment
- Tender Document Preparation
- Business Case Analysis
Challenges
Following the Grenfell Tower tragedy and a number of building fires linked to solar PV installations, the insurance industry has become increasingly concerned about the installation of solar PV on buildings.
Many insurers now publish requirements regarding the installation of solar PV on buildings, typically referring to fire safety guidance RC62.
Local fire safety experts specified the need for fire retardant fire breaks on flat roofs before solar PV could be installed, and there is no currently existing solution for this that could be found.
The project was ultimately able to overcome the issue by seeking advice from the insurer’s risk engineer, who agreed that fire isolation measures such as glass panels and solar edge inverters, alongside a stringent maintenance regime, were satisfactory to mitigate fire risk.
Results
Key successes of the project include:
- Over half of the sites included in the feasibility studies can proceed and have solar PV installed.
- The detailed feasibility enabled extensive investigative surveys, allowing for installation and design solutions, overcoming problems that may otherwise have stopped delivery.
- Essential fire safety, roof condition and structural surveys have ensured all additional measures are fully costed and included in the business case, therefore ensuring projects do not stall at a later stage due to unexpected costs without budget.
Combining all six sites where installation costs vary enables a consolidated business case that can deliver an acceptable Internal Rate of Return (IRR).
Lessons learned
Issues with fire retardant break requirements can be overcome with alternative mitigations, such as amending the specifications of the panels and installing a monitoring system.
Managing the projects as one cohesive portfolio introduced additional challenges as the risks of delay were higher, as the projects were all linked. For example, building survey information was difficult to obtain for some sites, which meant that others were held up due to this. However, by ‘pooling’ the sites in this way it meant that a more ambitious and innovative project can be taken forward and the carbon and energy savings generated will be greater.
Next Steps
The sites have now been approved at Exeter City Council’s Committee meeting and a procurement exercise will take place so that works can be commenced on all sites. They are scheduled to become operational in 2026.
If you work within a public sector organisation and would like a copy of the business case and accompanying reports produced, please contact swnetzerohub@westofengland-ca.gov.uk.